Alterations in the expression of the genes that control stem cell differentiation and self-renewal often contribute to tumorigenesis. Our laboratory has studied the mechanisms by which retinoids (vitamin A (retinol) and its derivatives and metabolites), control gene expression in both normal stem cells and in tumors. Over this past grant period we have developed evidence that: a) the polycomb group (PcG) protein(s) play a major role in repressing retinoid signaling in embryonic stem (ES) cells;b) these polycomb mediated inhibitory signals are altered in tumor cells;and c) specific retinoid receptors act in concert with transcriptional coactivators in a gene specific context. Our immediate goal in the next grant period is to delineate the mechanisms by which the polycomb group mediated transcriptional repressive pathways and the retinoid transcriptional signaling pathways intersect. Our Specific Aims for the next grant period: 1) We will elucidate the mechanisms by which the polycomb proteins inhibit retinoid transcriptional activation and retinoic acid induced cell differentiation. This will be accomplished by a combination of ChIP (chromatin immunoprecipitation) assays;overexpression or reduced expression of key transcriptional regulatory proteins such as pCIP (SRC3), EZH2, SUZ12, and JMJD3 in F9 and ES Wt and RAR1, 2, and 3 null cells;and deletion of DNA regulatory elements such as the Hoxa1 RARE, followed by analysis of PcG protein binding. We also propose a comparison of 3T3 cells with H-Ras transformed 3T3 cells to assess how an oncogenic protein perturbs retinoid signaling. 2) We plan to define the domains of the specific retinoic acid receptors (RARs) 1, 2, and 3 (i.e. the receptors for all-trans retinoic acid (RA) and other retinoids) and the coactivators for these receptors that control the transcriptional events which result in cell differentiation (and, thus, aid in inhibiting tumor cell proliferation). 3) Finally, as part of our goal of understanding retinoid regulation of stem cell differentiation, we will undertake a genome-wide search for primary target genes of the RARs through the use of ChIP-on-chip (tiling) arrays or ChIP-seq technology. This approach will allow us to obtain key information about the genes transcriptionally activated as ES cells differentiate along different pathways. For these proposed experiments we will utilize (a) murine ES and teratocarcinoma stem cell lines with both alleles of each of the individual RARs "knocked out" by homologous recombination;(b) ES cell lines with some of the "downstream" RAR target genes "knocked out";and (c) mice that have each of the individual RARs knocked out by homologous recombination. This proposed research will increase our knowledge of the molecular mechanisms by which signaling by retinoids is accomplished, provide new knowledge that will be useful for improvement of 'differentiation therapy'for cancer, delineate the mechanisms by which retinoids signal so that we will understand why some tumors are resistant to retinoid therapy, and allow us to manipulate the expression or function of polycomb repressive proteins to increase the effectiveness of retinoid based therapies and differentiation strategies for stem cells.